Recently a large number of digital cameras, which store images sensed by an image sensing element such as a CCD in a storage medium such as a memory card, are available on the market. A digital camera of this type, which does not require a film, stores an image signal sensed by the image sensing element in an external storage device, e.g., a CF card, hard disk and so on. Since such external storage device allows rewriting and erasing a number of times unlike films, expenses for the consumables can be kept low, which is very convenient.
Most of these digital cameras include an LCD monitor capable of displaying an image and a large-capacity memory such as a memory card. With the use of such digital cameras, not only films which have conventionally been used as consumables become unnecessary, but also outcomes of a photographed image can instantly be confirmed on the LCD monitor. Therefore, image data thought to be unnecessary by an operator can be erased in an instant, and an image can be photographed again if it is necessary. Digital cameras have enabled editing of an image stored in the memory at the scene of photographing, thus dramatically increasing the efficiency of photographing compared to silver chloride photographs.
On the contrary, conventional digital cameras have a problem. If a foreign substance, e.g., dust, which is unrelated to an object of shooting exists in the neighborhood of the image forming surface of the image sensing element such as a CCD (e.g., on the cover glass of a CCD), the image of the foreign substance is also photographed. A conventional silver chloride film also has the same problem of picking up an image of foreign substance if dust or the like exists on the film. However, in the case of a film, since film is moved every time one frame of photograph is taken, it is extremely rare to pick up the same dust on all frames.
However, in the case of the digital camera which senses an image with the image sensing element, since there is no mechanical movement after an image is photographed, once a foreign substance such as dust attaches to the image sensing element, there is a possibility that the dust is photographed on all frames after then. For this reason, an operator must always be careful about dust attachment to the image sensing element (CCD), and expends enormous effort in examining for the dust and cleaning. Particularly since the image sensing element (CCD) is arranged in the inner portion of the camera, examining for foreign substances is not easy.
In a digital camera of single lens reflex type, dust invasion easily takes place due to attachment and removal of the lens. Furthermore, in many cases of digital cameras of single lens reflex type, a focal plane shutter is arranged immediately before the image sensing element. Therefore, a mechanical operation of the shutter easily allows dust attachment to the image sensing element. Accordingly, it has been a great problem for a digital camera to identify and clean the dust attached to the image sensing element.
In view of this, digital cameras available on the market have begun to comprise a function (dusting mode) for identifying dust on the image sensing element using an LCD monitor, a function (cleaning mode) for removing foreign substances on the image sensing element by making the camera into a bulb state, and so on. Using the dusting mode of such digital camera enables easy identification of foreign substance attachment, e.g., dust, through an LCD monitor, or using the cleaning mode enables cleaning of the CCD cover glass surface from the lens mounting side.
However, the above-described conventional example has following problems.
During the cleaning mode operation, if the battery (portable electric power source) voltage declines to a level that cannot hold the rear curtain magnet of the shutter, the rear curtain of the shutter travels. More specifically, if the battery voltage declines causing the shutter rear curtain to travel while an operator removes dust or stain on the CCD surface from the lens mounting side using a cleaning tool such as a blower, the shutter is damaged and thereafter image sensing may become impossible. Since shutter repairing requires a high cost, damaging a sector is a great loss for a user.